How to make a vector structure globaly ?

We are developing a C++ project with 10 cpp files and 3 header files.We are declared array structure of 3 integer varibles globaly in header file and using in some files and where arrays are updated ,re-adjusted in some cpp files and use in another files.Project is running fine but we wish to use vector structure because dynamic allocation and easy resize.

How to replace array structure to vector structure ?
How to make a vector structure globaly ?